Associations of cataract, cataract surgery with dementia risk: A systematic review and meta-analysis of 448,140 participants

Author: Liu X, Guan Z, Liang S, Feng S, Zhou Y. 

Geographical coverage: Sweden, Taiwan, China, Italy, the USA and the UK

Sector: Cataracts, cataract surgery

Sub-sector: Risk of dementia

Equity focus: Not reported

Study population: Patients with cataract

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Dementia is a leading cause of disability and death worldwide and its prevalence is projected to rise to 152 million by 2050. Because effective treatments remain elusive, identifying modifiable risk factors is critical. Visual impairment appears to increase the risk of dementia. Cataract — a major cause of reversible visual impairment in older people — may play a role similar to hearing loss in the development of dementia. Although research on the association between cataract, cataract surgery and dementia has expanded, there is still no definitive evidence of causality. Given the effectiveness of cataract surgery, cataract may represent a modifiable risk factor for dementia.

Objective:

To examine the associations between cataract, cataract surgery and the risk of dementia, and to provide clinicians and researchers with up‑to‑date evidence relevant to dementia prevention and intervention.

Main findings:

The review included nine observational studies, encompassing 448 140 participants, published between 2014 and 2022. The studies were conducted in Sweden (n = 1), Taiwan/China (n = 2), Italy (n = 1), the USA (n = 3), China (n = 1) and the UK (n = 1). Methodological quality was rated moderate to high.

Meta‑analysis showed that cataract was associated with an increased risk of dementia (risk ratio [RR] 1.24, 95 % confidence interval [CI] 1.14–1.35, P < 0.00001). Conversely, cataract surgery was associated with a reduced risk of all‑cause dementia (RR 0.74, 95 % CI 0.67–0.81, P < 0.00001). These findings were consistent across subgroup and sensitivity analyses.

Methodology:

Searches were conducted in Medline, Embase and CENTRAL up to 22 April 2023 to identify cohort or nested case‑control studies assessing the relationships between cataract and/or cataract surgery and dementia risk. There were no language or follow‑up restrictions. Two reviewers independently screened and extracted data, resolving disagreements through discussion or consultation with a third reviewer. Study quality was assessed using the Newcastle–Ottawa scale.

Results were synthesised using a random‑effects meta‑analysis. Heterogeneity was assessed with Cochrane’s Q test and I² statistics. Subgroup analyses explored potential sources of heterogeneity and sensitivity analyses tested the robustness of the findings.

Applicability/external validity:

The evidence base comprised only nine observational studies, none of which were randomised controlled trials. This limits the ability to draw definitive causal conclusions about cataract, cataract surgery and dementia. The review underscored the need for further research to determine whether cataract is an independent risk factor for dementia.

Geographic focus:

No geographical limits were applied. The included studies were from Sweden, Taiwan, China, Italy, the USA and the UK.

Summary of quality assessment:

Confidence in the conclusions is rated as medium. Database searches were comprehensive and inclusion and exclusion criteria were clearly defined. Two reviewers independently screened and extracted data, and methodological quality was assessed using established tools. Characteristics of included studies were well documented, meta‑analyses were conducted appropriately, and heterogeneity was addressed. However, the review did not provide a list of excluded studies, report whether reference lists were checked or specify whether findings were reported by risk‑of‑bias status. Only observational studies were included, and no assessment of contact with study authors or experts was reported.